How to install and use flutter_bloc with Flutter 3.10.5 - including code sample!

You can either add the package directly using the flutter command line.

$ flutter pub add flutter_bloc

Or add the dependency directly to your pubspec.yaml file.

dependencies:
  flutter_bloc: ^8.1.3

In either case, make sure to refresh your packages by running the following command:

$ flutter pub get

Once you have installed the package, you can use it in your Flutter application by importing it.

import 'package:flutter_bloc/flutter_bloc.dart';

// ignore_for_file: avoid_print

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

void main() {
  Bloc.observer = const AppBlocObserver();
  runApp(const App());
}

/// {@template app_bloc_observer}
/// Custom [BlocObserver] that observes all bloc and cubit state changes.
/// {@endtemplate}
class AppBlocObserver extends BlocObserver {
  /// {@macro app_bloc_observer}
  const AppBlocObserver();

  @override
  void onChange(BlocBase bloc, Change change) {
    super.onChange(bloc, change);
    if (bloc is Cubit) print(change);
  }

  @override
  void onTransition(
    Bloc bloc,
    Transition transition,
  ) {
    super.onTransition(bloc, transition);
    print(transition);
  }
}

/// {@template app}
/// A [StatelessWidget] that:
/// * uses [bloc](https://pub.dev/packages/bloc) and
/// [flutter_bloc](https://pub.dev/packages/flutter_bloc)
/// to manage the state of a counter and the app theme.
/// {@endtemplate}
class App extends StatelessWidget {
  /// {@macro app}
  const App({super.key});

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (_) => ThemeCubit(),
      child: const AppView(),
    );
  }
}

/// {@template app_view}
/// A [StatelessWidget] that:
/// * reacts to state changes in the [ThemeCubit]
/// and updates the theme of the [MaterialApp].
/// * renders the [CounterPage].
/// {@endtemplate}
class AppView extends StatelessWidget {
  /// {@macro app_view}
  const AppView({super.key});

  @override
  Widget build(BuildContext context) {
    return BlocBuilder(
      builder: (_, theme) {
        return MaterialApp(
          theme: theme,
          home: const CounterPage(),
        );
      },
    );
  }
}

/// {@template counter_page}
/// A [StatelessWidget] that:
/// * provides a [CounterBloc] to the [CounterView].
/// {@endtemplate}
class CounterPage extends StatelessWidget {
  /// {@macro counter_page}
  const CounterPage({super.key});

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (_) => CounterBloc(),
      child: const CounterView(),
    );
  }
}

/// {@template counter_view}
/// A [StatelessWidget] that:
/// * demonstrates how to consume and interact with a [CounterBloc].
/// {@endtemplate}
class CounterView extends StatelessWidget {
  /// {@macro counter_view}
  const CounterView({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Counter')),
      body: Center(
        child: BlocBuilder(
          builder: (context, count) {
            return Text(
              '$count',
              style: Theme.of(context).textTheme.displayLarge,
            );
          },
        ),
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: [
          FloatingActionButton(
            child: const Icon(Icons.add),
            onPressed: () {
              context.read().add(CounterIncrementPressed());
            },
          ),
          const SizedBox(height: 4),
          FloatingActionButton(
            child: const Icon(Icons.remove),
            onPressed: () {
              context.read().add(CounterDecrementPressed());
            },
          ),
          const SizedBox(height: 4),
          FloatingActionButton(
            child: const Icon(Icons.brightness_6),
            onPressed: () {
              context.read().toggleTheme();
            },
          ),
        ],
      ),
    );
  }
}

/// Event being processed by [CounterBloc].
abstract class CounterEvent {}

/// Notifies bloc to increment state.
class CounterIncrementPressed extends CounterEvent {}

/// Notifies bloc to decrement state.
class CounterDecrementPressed extends CounterEvent {}

/// {@template counter_bloc}
/// A simple [Bloc] that manages an `int` as its state.
/// {@endtemplate}
class CounterBloc extends Bloc {
  /// {@macro counter_bloc}
  CounterBloc() : super(0) {
    on((event, emit) => emit(state + 1));
    on((event, emit) => emit(state - 1));
  }
}

/// {@template brightness_cubit}
/// A simple [Cubit] that manages the [ThemeData] as its state.
/// {@endtemplate}
class ThemeCubit extends Cubit {
  /// {@macro brightness_cubit}
  ThemeCubit() : super(_lightTheme);

  static final _lightTheme = ThemeData(
    floatingActionButtonTheme: const FloatingActionButtonThemeData(
      foregroundColor: Colors.white,
    ),
    brightness: Brightness.light,
  );

  static final _darkTheme = ThemeData(
    floatingActionButtonTheme: const FloatingActionButtonThemeData(
      foregroundColor: Colors.black,
    ),
    brightness: Brightness.dark,
  );

  /// Toggles the current brightness between light and dark.
  void toggleTheme() {
    emit(state.brightness == Brightness.dark ? _lightTheme : _darkTheme);
  }
}